The present invention relates to a brake system with brake slip control provided for automotive vehicles, in particular for road vehicles, wherein each one front wheel and one rear wheel are assigned to one joint braking pressure control channel, and wherein the individual wheels and/or the axles are equipped with sensors for the determination of the wheel rotational behavior, the output signals of said sensors serving after their electronic combination and processing to control braking pressure modulators, e.g. solenoid valves.
It is known already for simplification and cost reduction of such brake systems equipped with brake slip control to control not all vehicle wheels individually but to expose for instance the rear wheels to the same amount of braking pressure. In order to avoid locking of both rear wheels in this case nevertheless, according to the "select-low" principle, the wheel at which greatest deceleration occurs will be chosen for dimensioning the braking pressure. It has to be put up with in this respect that the maximum possible exploitation of friction of the second co-controlled wheel will not be attained in the majority of cases--same friction provided on both sides--as a result whereof the stopping distance necessary may become longer.
If, on the other hand, the brake slip control is based on the "select-high" principle of the faster or the less decelerated wheel, this will in some cases have as a consequence too high slip or locking of the co-controlled wheel. Both "select-low" and "select-high" selection principles have specific advantages and shortcomings which appear as a function of road conditions.
Moreover, it is known to depart from the described invariable allocation of wheels to a specific control group for which either "select-low" or "select-high" applies. For example, in a known system the anti-locking system the wheel having worst road contact is determined, its rotational behavior is discounted and all remaining wheels are controlled jointly pursuant to the "select-low" criterion. In the event of a diagonally split-up dual-circuit brake system, with this known system, the circuit corresponding to the wheel that becomes instable first is switched to "select-high", while the other circuit will be switched to "select-low". This method has the disadvantage that under unfavorable conditions, e.g. in the event of icy roads or aquaplaning, when both front wheels tend to lock, there will result an excessive reduction of the braking effect and hence a too long of a stopping distance.
It is therefore an object of the present invention to over these and other disadvantages and to provide a brake system with brake slip control which, despite the restriction to two braking pressure control channels, ensures reliable braking at a shortest possible stopping distance even under unfavorable road conditions i.e., at low friction due to ice or aquaplaning, fresh-fallen snow or the like.